It has become common for some people to put oversize rear tires on motorcycles. Technically, these larger rear tires will provide more grip for a user (especially in straight line acceleration), which is often desirable as motorcycles become more and more powerful. However, in many cases, the motorcycle owner simply likes the appearance of the motorcycle with a wider rear tire.
It has become common to see rear wheels and kits for motorcycles that allow rear tires up to 8″ or more in width to be added to a motorcycle. Typically, these kits include a rear frame for the rear wheel that replaces the stock rear frame on the motorcycle. The belt running from the transmission to the sprocket on the rear wheel is usually moved further out to the side of the motorcycle in order to clear the new wider rear wheel.
However, moving the belt out further to the side of the motorcycle has disadvantages. For example, moving the belt further out from the transmission makes it stick out that much further from the side of the motorcycle and creates a greater risk of something getting hit or caught by the belt (such as the ankle or leg of a rider). This is even more dangerous when you consider that while the motorcycle is in motion this belt is often moving quite fast. In addition, the further the belt is moved out from the side of the motorcycle the more offset the power being transferred to the rear wheel of the motorcycle which can cause a number of complications. The width of rear wheel that can be used is also limited by the amount this belt can be moved out to the side of the motorcycle so that it clears the new wider rear wheel of the motorcycle.
Some rear wheel assemblies for motorcycles have been designed that split the rear wheel of the motorcycle so that two separate tire sections are present and the drive train used to drive the rear wheel passes between the two separate tire sections. U.S. Pat. No. 4,003,443 to Boughers and PCT Published App. WO99/50133 to Nemeth both show motorcycles with the rear wheel separated into two tire sections in this manner. However, in order to allow the motorcycle to be leaned during a turn by a rider, both of these devices require extensively modified rear suspensions. In Bougers the suspension allows the two tires to move independently from each other in a vertical direction during the turn, while in Nemeth the rotational plane of the tires remains vertical, and the suspension allows the motorcycle frame to tilt with respect to the tires.